This invention relates to compounds, compositions and methods of using the compounds and compositions as traction fluids in toroidal continuously variable transmission (T-CVT) systems.
A T-CVT system includes an input disk connected to the engine, an output disk connected to the wheels, and a pair of power rollers which engage the two disks and transfer drive power from the input disk to the output disk. A lubricant, called a traction fluid, lubricates the system and prevents the rollers from contacting the disks. Because the disks and roller never physically touch, the traction fluid also transfers drive power from the input disk to the rollers and then to the output disk. This contradiction of purposes leads to the adversarial nature of the physical properties needed by a traction fluid.
One constraint is the ability of any particular traction fluid to transfer power among the components of the T-CVT system. This ability is represented by the traction coefficient (xcexcT). The drive power is directly proportional to the xcexcT, thus a higher xcexcT is advantageous.
Another constraint on the physical properties of a traction fluid is the range of temperatures at which a T-CVT must be operational. Start-up operating temperatures of T-CVT""s may be as low as xe2x88x9240xc2x0 C., while operating temperature could be as high as 140xc2x0 C. Normal operating conditions will be in the range of 90xc2x0 to 110xc2x0 C. At the low end of the temperature range, the traction fluid must have a viscosity which is low enough to allow the traction fluid to flow and be pumped. At the high end of the range, the viscosity must be high enough to provide adequate lubrication. A flash point above 150xc2x0 C. is desirable. In between the extremes of temperature, it is desirable to have the xcexcT of the traction fluid independent of temperature. Furthermore, the viscosity of the traction fluid at the normal operating temperature is such that the fluid is retained on the rollers and disks of the T-CVT.
Traction fluids that are non-toxic to humans and posses a non-offensive odor, while also being inexpensive to manufacture are desirable.
While the large and heavy nature of T-CVT systems can be problematic, they do offer advantages that make them desirable, especially in terms of providing greater fuel economy in vehicles and machines. Generally, T-CVT systems provide at least 10% fuel efficiency over traditional automatic transmissions because the engine runs at its most efficient point independent of the vehicle speed. Since the traction fluid is responsible for the transfer of power to the wheels, the efficiency of a T-CVT system is related to xcexcT and viscosity of the utilized traction fluid. Further, an increase in efficiency also allows for the reduction in size and weight of the T-CVT system.
Known traction fluids do not have acceptable physical properties. Particularly, some known traction fluids have a high xcexcT at normal operating temperatures, but unacceptably high viscosities at low temperatures. Other known traction fluids have good low temperature viscosities, but the xcexcT is unsatisfactory. Still other traction fluids have xcexcT which are unacceptably dependent on temperature. Most known traction fluids suffer from difficult, expensive, and inefficient synthetic methods.
Exemplary known traction fluids include those based on 2,4-dicyclohexyl-2-methylpentane (DCMP) [CAS# 38970-72-8], which has a structure of: 
Another known traction fluid is made from santene and isosantene (called FLUID X). The structure of the main component of this traction fluid is as follows: 
Accordingly, the inventors have recognized a new class of traction fluids which overcome one or more of these problems which allow more efficient T-CVT systems.
The present invention includes a traction fluid that includes an alkyl bridged dimer of bicycloheptane. Methods of using alkyl bridged dimers of bicycloheptane in traction fluids are also disclosed.